Bhagvad Gita IV:24

To my mind this verse is an expression of the exceptional brilliance of the religious elite, the author(s) of the Gita. I have mentioned before that the Gita is a pivotal text, bridging 'old' Vedic ideas and 'new' Bhakti influences. How to reconcile the Vedic sacrifice (which was completely about external action and compelling Vedic gods to attend to the yajamāna)  with the 'new' thinking of the Upaniṣads, whose focus was internal, and monistic? How to bring on board the old school, and avoid a schism in the religious community? This verse shows how to achieve the impossible. How to amalgamate opposites. 

ब्रह्मार्पणं ब्रह्म हविर्

ब्रह्माग्नौब्रह्मणा हुताम्

ब्रह्मैव तेन गन्तव्यं 

ब्रह्मकर्मसमाधिना

Brahman is the offering, Brahman is the oblation Poured by Brahman into the fire of Brahman; Brahman is to be attained by him, who always contemplates (sees) Brahman in action.

ब्रह्म - Brahman (neut., nom., sing.) 

अर्पणम् - offering (neut., nom., sing.)

ब्रह्म - Brahman (neut., nom., sing.)

हविस्  - oblation [poured into havan] (neut., nom., sing.)

ब्रह्म - Brahman (neut., nom., sing.)

अग्नौ - in the fire (masc., locative, sing.) 

ब्रह्मणा - Brahman (neut., nom., sing.) - by Brahman (neut., instrumental, sing.)

हुतम् - poured into the sacrifice (masc. accusative, sing, past participle √hu)

ब्रह्म - Brahman (neut., nom., sing.)

एव- only (avyaya)

तेन - by him (masc., instrumental, sing.)

गन्तव्यं - [it is] to be attained, approached, reached, gone to (gerundive of  √gam)

ब्रह्मकर्मसमाधिना - by [him/one] who contemplates the action of Brahman. (masc., instrumental, singular, bahuvrihi compound)

"The entire act consists of Brahman because it is of Brahman's nature: the sacrifice is Brahman the utensils are Brahman, the fire in which the sacrifice is offered is Brahman, the sacrificer himself is Brahman. He who contemplates this insight, contemplates the act-as-Brahman.Such a one is capable of knowing the proper form of atman - which is Brahman - through his acts, because his acts are of Brahman's nature. ..." From Ramanuja, translated by van Buitenen